Project I's overall goal is to develop evidence-based definitions of 3 specific language disabilities in written language (SLDs-WL): Impaired Handwriting; Impaired Word Reading/Spelling; Impaired Reading Comprehension/WrittenExpression. Research Aim 1 is to test Hypothesis 1 that the prior findings of relationships between unique impairments in Learning Profiles (patterns of impaired and non-impaired reading, writing, and oral language skills) and unique impairments in Phenotype Profiles (working memory storage and processing units, loops, and executive functions for supervisory attention), replicate. Research Aim 2 is to test Hypothesis 2 that each ofthe 3 SLDs-WL will differentially predict response to intervention (RTI) during the portion of the specialized instruction tailored to the nature of the impairment in a specific SLD-WL: slower RTI and less stability on written language outcomes for its defining impairment(s) compared to the other 2 SLDs-WL and controls from pretest to posttest (following specialized instruction) to long-term follow-up 1 (about a year later) and follow-up 2 (about 2 years later). Specific Aim 3 is to test Hypothesis 3 that professional development of teachers will improve language learning and phenotype skills further and/or maintain them if next year's language arts teacher receives professional development on language, executive functions, and differentiated instruction after follow-up 1; to test it, student outcomes between long- term follow-ups 1 and 2 will be compared. Specific Aim 4 is to test Hypothesis 4 that interdisciplinary variables explain RTI better (explain unique variance and more variance) than variables from a single discipline: motivation, brain, gene, working memory phenotype, and language learning measures will be used as predictors in cross-center multiple regressions of longitudinal RTI. To accomplish its research aims. Project I will work closely with Projects II, III, and Administrative Core A and Service Core B.